1. Field of the Invention
The invention is related generally to the field of electronic and optoelectronic devices, and more particularly, to suppression of inclined defect formation and increase of critical thickness by Silicon (Si) doping on non-c-plane (Al,Ga,In)N.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [Ref. X]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Despite recent progress, the performance of green light emitting diodes (LEDs) and laser diodes (LDs) is much lower than equivalent devices emitting in blue or violet regimes. Active regions operating in the green regime require Indium (In) compositions in the quantum wells (QWs) of around 30%. Due to the large lattice mismatch between InN and GaN of around 10%, such structures must be grown at very high strain, e.g., 3% for In0.3Ga0.7N, thereby degrading crystal quality and leading to large piezoelectric induced electric fields in the quantum wells. Stress relaxation also limits the composition and thickness of InGaN waveguiding layers in LDs [Ref. 1].
For traditional planar c-plane and nonpolar strained heteroepitaxy, stress relaxation typically does not occur via slip due to the absences of resolved shear stress on the c-plane, which is the most favorable slip system. However, c-plane slip has been observed on (20-21) and (11-22) semipolar orientations, which have significant resolved shear stress on the c-plane [Ref 2].
An available stress relaxation mechanism which preserves the crystal quality of overlying layers opens up the possibility of growing relaxed InGaN buffers. Aside from reducing active region strain during growth, an InGaN virtual substrate would open up device design space by allowing for tensile strained or unstrained InGaN barriers to reduce band offsets, reduced piezoelectric polarization in the QWs, and increased critical thickness for InGaN waveguiding layers. Moreover, c-plane slip can only relieve stress parallel to the c-plane, and at higher layer thicknesses and compositions, the stress in the orthogonal direction will eventually lead to relaxation by another mechanism.
AlGaN films can relieve this strain via cracking, but this mechanism is not available in InGaN due the compressive nature of the epi-strain. At thicknesses sufficiently beyond the critical thickness, dark lines are observed inclined with respect to the c-direction. For (20-21) InGaN, these lines are parallel to the intersection of the growth plane with inclined m-planes, and in (11-22) InGaN, lines have been observed parallel to the intersection of the growth plane and inclined m- and a-planes. These lines are likely misfit dislocations (MDs) formed by slip on the inclined m-planes and/or a-planes.
FIG. 1 is a cathodoluminescence (CL) image of 500 nanometers (nm) of In0.03Ga0.97N on a (20-21) GaN substrate, showing dark dots 100, and wherein c-plane and m-plane slip lines 102, 104, respectively, are visible in the background, and m-plane slip lines 106 are visible in the foreground. In FIG. 1, inclined lines 104, 106 are at an angle less than 90° with respect to the in-plane a-direction, and line 102 is parallel to the a-direction. As shown in FIG. 1, interaction between the misfit dislocation lines from c-plane and m-plane slip leads to threading dislocation (TD) multiplication, as seen by the dark dots 100 decorating the inclined lines 104, 106. The dark dots 100 at the intersection of the c-plane and m-plane slip lines are newly formed TDs with a density greater than 1×108 cm−2, wherein substrate TD densities are on the order of 0.5-1×107 cm−2.
Once formed, TDs are very difficult to remove and have deleterious consequences for subsequently grown devices, in contrast to the misfit dislocation lines formed by slip, which can easily be buried far from the active region and have negligible impact on device performance. Thus, avoiding TD formation is highly desired and critical to achieving improved device performance using relaxed buffer layers.
Thus, there is a need in the art for improved methods for preventing the formation of additional TDs. The present invention satisfies this need. Specifically, the present invention shows the impact of Si doping on defect morphology and prevention of additional TD formation.